Vortec heads Tech Questions Answered - Ask Anything

Goodwrench Question

Terry Hagen; Cornelius, OR: Longtime reader (as in “Honk” if you remember), first time writing in. First, I’d like to say project Sten is about as perfect and spot-on a project as you could have come up with. It really brings up memories of what the essence of what hot rodding really is. Stuff a V8 into something small, fun, and that we can get parts for. Make it street legal so we can actually drive it. Keep Sten rolling—I love it!

Here’s my question. I have a ’69 GMC pickup that is need of a new motor. It currently has a 0.040-over 350 that is equipped with cam, lifters, heads, intake, carb, headers, and exhaust. I liked the article you wrote up on the basic 290hp GM replacement long-block and its potential, while remaining very affordable. I’m wondering if the Vortec small-block would be a better choice at only $300 or $400 more? What problems would I encounter swapping in this motor, other than the intake manifold and fuel pump? What electric fuel pump would be a good choice?

Jeff Smith: Thanks for the comments on the Sten. It has been on the back burner longer than planned while we worked through a bunch of engine testing and Chevelle flogging, but now that I have some time, we can get back on the beast. Look for details soon.

To address your question, the engine we used was the GM Goodwrench replacement 350 from Scoggin-Dickey in Lubbock, Texas—not the 350 HO engine. The Goodwrench 350 (PN 10067353; $1,499.95, Scoggin Dickey) is a brand-new engine using the older, two-piece rear main seal block and crank along with a flat-tappet camshaft. The engine is rated at 245 hp and has a very mild hydraulic flat-tappet camshaft. It has generic 1.94/1.50-inch-valve small-block heads with 76cc chambers. The engine you referenced (PN 12499529) is a 290hp 350 engine long-block. It also uses the older-style, two-piece rear main seal, flat-tappet hydraulic camshaft, and 76cc combustion chamber heads. The increased horsepower is mainly due to the longer 222/222 degrees of duration camshaft that sports 0.450/0.460-inch lift, which is much more lift and duration than the Goodwrench engine. Scoggin-Dickey sells the 12499529 long-block for $1,999.95, which is $500 more for the addition of a longer-duration camshaft that you could do yourself (though that would affect the warranty). The long-block that has the best potential is the 290hp 350ci with the iron Vortec heads (PN 19210007, $2,899.95). But as you can see, this involves a significant price jump of roughly $900. If you’re willing to do a little parts-swapping, there is an alternative that involves using the best parts of these engines. First, we’d start with the basic Goodwrench engine and then add a pair of iron Vortec heads. The least expensive version is the stock Vortec heads (PN 12558060; $619.90, Scoggin-Dickey), but you do have to modify them to accept more than 0.450-inch valve lift—more on that in a minute.

As you know, these heads will require a specific Vortec intake manifold. We usually choose the Edelbrock Performer RPM Vortec (PN 7116; $189.95; Summit Racing). You could go with the stock 222/222-degree camshaft, but this is a single-pattern cam, and the Vortec exhaust ports are not quite as good as the intakes are, so a dual-pattern cam with more lift and duration on the exhaust lobe is a better choice to help make a little more power.

We used a very inexpensive cam from Summit Racing on our Goodwrench test, which worked very well. The cam is PN SUM-1105, and the specs are 224/234 degrees at 0.050 with 0.465/0.485 lift and a 114-degree lobe-separation angle. When we did our Slayer story in the May ’12 issue, the cam was $54.95, but when we re-checked the price, Summit has reduced it to $49.95. In addition, if you replace the cam before starting the engine, you can use the brand-new GM lifters and save even more money. This will require modifications to the Vortec heads, because the stock valvesprings cannot handle this additional lift, especially on the exhaust side. So if you decide to go with this bigger cam, we’d suggest ordering Scoggin-Dickey’s modified version of the Vortec heads. Scoggin-Dickey machines the valveguides to improve the retainer-to-seal clearance and adds a set of Z28 springs that allow the heads to accept valve lift up to 0.525 inch, which is more than enough for that Summit camshaft. These modified heads (PN SD8060A2; $779.90, Scoggin-Dickey) are a simple bolt-on and are certainly worth the $180 additional price over the stock Vortecs. Adding the bigger cam should put this package at roughly 350 to 360 hp, which is really good power considering the inexpensive components. The Vortec heads automatically improve the compression with their 64cc chambers instead of the 76cc heads that come stock with the Goodwrench engine. Another step you could take—as we did on our Slayer engine—is to switch to Fel-Pro 1094 head gaskets, which are thinner at 0.015 inch and will help pump the compression up to around 9.4:1. This would make a great package with excellent street manners and great torque, and it would deliver consistently good power for as long as you wanted to drive it. These changes to the basic Goodwrench engine will cost about $2,600, but they will help to make more power than the 290hp Vortec GM package and will save you about $300! Of course, you’ve also lost some of the warranty, and to some that might be worth $300. At least you have plenty of choices.

As for a fuel pump, there are probably dozens to choose from since 350 to 375 hp doesn’t require a tremendous amount of fuel volume. The classic Carter rotary vane (PN GP4070; $81.95, Summit Racing) or the Holley red pump (PN 12-801-1; $108.95; Summit Racing) are both capable of delivering sufficient fuel volume and neither requires a fuel-pressure regulator, keeping the price down.

Low-Rev Pontiac

Roger Miller; Farmingdale, NY: First of all, I have been a loyal subscriber for more than 20 years. I have cancelled other subscriptions but have always kept Car Craft.

I have a ’76 Trans Am with a Pontiac 400 motor. The motor is not original but is stock (year unknown), with stock intake and exhaust manifolds, Rochester Q-jet carb, and so on. It has 6H heads, which I believe came on 455s. It has a dual-exhaust setup without cats.

The problem is the engine will not rev past 3,200 rpm, even in Park, so it’s not related to the trans or rear end. When I floor the gas pedal, the motor revs to about 3,200 and then levels out. The motor seems to have decent power, and there are no other problems. I have checked the carb, and the throttle is opening all the way. I have been advised of a few possible causes: weak valvesprings, too low a compression ratio (400 motor with 455 heads = under 8.0:1), distributor timing/advance needs to be changed, carb secondaries not opening. What should I check first?

Jeff Smith: Over the years, Roger, I’ve found that it’s best to eliminate the easily fixable problems first when performing a diagnosis. There’s nothing more humbling than doing a major repair only to discover that the real reason was the throttle wasn’t opening all the way. Be sure that the choke lock on the passenger side of the carb has released the secondary linkage. The Q-jet uses a small lever on the secondary side that can be locked by the choke linkage to prevent the secondaries from opening when the choke is engaged. The linkage will make it feel as though the secondaries are opening, but you have to look inside the carburetor to make sure.

This would also be a great time to check initial and total mechanical advance. You can do this even if you don’t have a dial-back timing light. The easiest way is to buy an MSD timing tape (PN 8985; $4.95, Summit Racing) intended for the diameter of your balancer. If you don’t want to wait, you can make your own with a length of masking tape and a one-sixty-fourth graduated ruler. If your balancer is 8 inches in diameter, that makes the circumference 25.13 inches. Divide that by 90, and every 4 degrees will be 0.279 or nineteen-sixty-fourth of an inch. Mark off these graduations from zero to 40 degrees and lay the tape on the balancer with the zero mark in line with the zero mark on the balancer. Be sure to disconnect the vacuum-advance line from the carburetor, and with the transmission in Neutral or Park, rev the engine to 2,800 to 3,000 rpm. You should read around 36 degrees. If the number is much higher or lower, try adjusting the initial timing to compensate. If the engine runs worse after adjusting, then you need to check for the proper position of top-dead center (TDC).

The best way to check for TDC is to remove all the spark plugs and use a spark plug–style piston stop. Put the stop in the No. 1 cylinder, and then, by hand, very carefully rotate the engine clockwise until the piston hits the stop. Do not bump the engine with the starter, as that’s a good way to break a piston! Mark the balancer where the piston stopped, and then rotate the engine in the counterclockwise direction until you hit the stop. Mark that position and then measure to see if TDC on the balancer is exactly halfway between the marks. If not, the TDC mark on the balancer is incorrect. Often what happens is that the ring on the balancer has rotated on the hub, thereby creating the discrepancy. I suspect you’ll find the ignition timing is correct, or within range. This will likely lead us to what I think is the real cause of your problem: the valvesprings. But let’s try one more thing. With all the spark plugs removed, check the cranking compression. It should be between 160 and 180 psi. If the pressure is way down but consistent throughout all eight cylinders, it’s possible that the timing chain is very loose and has skipped a tooth. This would radically affect cam timing and perhaps cause your problem. Since you said the engine seems to run acceptably below 3,200, I think the valvesprings are the real culprit.

The best way to confirm this is the problem is to test one of the existing springs, before replacing all 16. You will need a source of compressed air, a spark-plug hose adapter to put the air in the cylinder (similar to what’s used on a compression tester), a valvespring compressor, and a checking spring. Once you have air in the cylinder, tap the valvespring retainer with a rubber hammer to help loosen the retainer locks. For your engine, a lever-type valvespring compressor tool will work, but we’ve also had good luck with the type that clamps on the outside of the spring and uses a knob that, when tightened, compresses the spring. Once you’ve removed the locks, retainer, and spring, place a lightweight checking spring in the spring pocket and reuse the locks and retainer. This way, you don’t have to rely on air to keep the valve in place. Next, take the old valvespring to your local machine shop and have them measure the spring pressure. Stock specs are generally around 100 pounds on the seat at the normal installed height of 1.60 inches. The installed height is the distance from the spring seat on the head to the underside of the retainer with the valve fully closed. A machinist’s rule will get you close enough on this measurement. Give that installed height to the machine shop, and they can measure the closed spring pressure. Valve-open pressure should be around 220 to 230 pounds at 0.500-inch valve lift. I think you will find the old spring pressure is down to maybe 60 or 70 pounds on the seat (and perhaps less) with roughly 140 pounds open. This poor spring pressure allows the valves to bounce off the seat when closing and won’t allow the engine to rev past 3,200. If you find the spring pressure is low, I’d suggest replacing all the springs. This will require measuring the installed height and possibly adding shims to ensure the height is the same for all 16 springs. This will certainly help engine performance. Stock replacement springs will suffice, as there’s no reason to install heavier springs since the cam is stock.

If the spring pressure is within acceptable range of at least 90 to 100 pounds on the seat, then I would check a second spring elsewhere in the engine. If that spring also checks good, then it’s possible the cam has gone flat. The best way to check is with a dial indicator on the valvespring retainer to measure lift. Even a stock cam should be able to generate 0.380 inch of valve lift. If the lift numbers are way down, you’ve found your problem! But my money is on the valvesprings.

Head Flow Under Pressure

Trevor Kertson; Silverton, OR: I am particularly interested in articles and tech answers regarding cylinder heads. This brings me to my question: Does anyone know what type of effect supercharging (turbo, roots, etc.) has on the way a cylinder head flows? I understand that, generally speaking, cylinder heads are tested at a certain depression (vacuum) of atmosphere, and this may not be identical from one tester (or manufacturer) to another.

I am aware of the wet-flow testing that is being done on some aftermarket heads, but I know this is done with vacuum and not pressure. Perhaps I am overthinking this whole thing, but I currently think that a cylinder head optimized for naturally aspirated operation could be optimized in a different manner for a supercharged operation.

Jeff Smith: Some enthusiasts think that using a supercharger or some kind of forced induction minimizes the need for a good cylinder head because the boost is a cure-all. While the inlet pressure does push the air and fuel in, anything that will help airflow for a normally aspirated engine will also improve power. It turns out that a weak set of heads, especially on the exhaust side, can have a detrimental effect on the supercharger’s ability to make power. I subscribe to what my friends like to call the Louie Hammel Funnel Theory. Louie is a very sharp internal-combustion-engine tech head who once described a supercharger as functioning like a funnel, directing a maximum amount of (in our case) air and fuel into the engine. But power potential is often limited by the exhaust side of the cylinder heads, which in this analogy is the restricted outlet of the funnel. If you want to flow more water (or air and fuel), you need to open up the restriction—the exhaust side. You can bolt on a very large supercharger, but if the exhaust ports are restricted in flow, the results will be disappointing.

You asked whether the cfm coming into the engine needs to be equal to the cfm coming out. It would appear on the surface that this would be true. But consider that the inlet side on a normally aspirated engine is only using atmospheric pressure to push the air and fuel. The air is relatively cool and is not under great pressure. Conversely, when the exhaust valve opens, the combusted mixture is very hot and still under significant pressure. This pressure helps to push the mixture past the exhaust valve. Later in the exhaust cycle, the piston also assists with pushing the exhaust gas out. That is why the exhaust valve can be roughly 20 percent smaller than the intake valve and still do a good job of venting the exhaust gas. But the valve is only a portion of the requirement. A very important element is the shape of the exhaust port. A very well-designed exhaust port can help evacuate the cylinder of spent combustion gases, which improves power everywhere, but especially at higher engine speeds where there is less time (both in exhaust lobe duration and actual physical time) to vent the cylinder.

1/2The most common flow bench on the market right now is the SuperFlow 600 bench that is capable of flow testing heads well over 400 cfm at 28 inches of water. There are more expensive benches, but this has become virtually the industry standard.

Based on thousands of dyno tests on lots of different engines, a general rule of thumb is that if the exhaust port on a flow bench can flow roughly 70 percent of the intake-port flow at the same valve lift, the head will generally work well. Of course, this is a very general description with several caveats. For example, if the cylinder head has a weak intake port, even a poor-performing exhaust port can generate a 70 percent exhaust to intake (E/I) percentage. What we’re looking for is a balance between the intake and exhaust-port flow. For example, if you have a hero intake-port-flow number, like 280 cfm at 0.500-inch valve lift, the exhaust port has to perform as well. Using our 70 percent evaluation, the exhaust port should flow somewhere around 195 cfm or greater in order to achieve this percentage (280 x 0.70 = 196 cfm). Certainly, flow numbers exceeding this percentage are not bad, but it is important to keep this percentage in mind because it helps when deciding on camshaft specs. If the exhaust port performs at 70 percent or higher throughout the entire valve-lift curve, it’s a good indication that the engine will respond better to a single-pattern camshaft on which the intake and exhaust lobes are the same duration numbers. Conversely, a cylinder head with poor E/I percentages will generally work better in an engine fitted with a dual-pattern camshaft with more exhaust duration compared with the intake. Even cylinder heads with good E/I numbers will often produce better peak horsepower numbers with longer exhaust duration numbers mainly because of the limited amount of time available to push the exhaust out of the cylinder at very high engine speeds (above 7,000 rpm).

You also asked about flow numbers and the danger of comparing flow numbers of different heads flowed on different benches. Several years ago, we embarked on a quest to flow as many small-block Chevy cylinder heads as possible on the same flow bench while minimizing the variables between tests. While the most popular test depression is 28 inches of water, there are many other variables that can drastically affect flow numbers. The most obvious is fitting the exhaust port with a flow tube. This simulates the use of a header pipe and will often deliver 5 percent or more flow increases with no other changes. So when evaluating a cylinder head, you need to know whether the head was fitted with an exhaust-flow tube. It goes without saying that the intake port should always be fitted with a radius entry, but we still run across tests in which this is not done. Another favorite trick with flow-bench testing is to use a very large bore diameter. Again using our small-block Chevy example, if all we do is change from a 4.00-inch bore sleeve to a 4.155-inch bore in the flow bench, intake flow will especially increase by several percentage points. With a 250-cfm intake port, that could be worth 5 or more cfm. This is simply due to moving the cylinder wall away from the intake valve and allowing the air a less restrictive path in to the cylinder. This is not a flow-bench cheat. The flow bench is merely indicating what will happen if you place that cylinder head on a larger-bore engine. This is why big-bore engines are so popular in drag racing. The important thing to remember when comparing flow numbers is to make sure the heads you are comparing were all tested on the same bore adapter. If not, you need to take that into account in the comparison.

Each family of cylinder heads has its advantages and disadvantages. One reason the new-generation LS engines are so popular is because this family has tremendous flow potential on both the intake and exhaust side. This makes the heads very balanced components. The Mod motor Fords are also popular because of their multiple valves. Stuff two small intake and exhaust valves in the same-size cylinder bore, and you radically increase the flow area. This is commonly called the flow curtain and is a function of valve diameter x pi x valve lift. Let’s take an LS3 with a huge 2.16 intake valve at 0.600-inch valve lift. Valve diameter multiplied by pi equals the circumference of the valve: 2.16 x 3.1417 = 6.78 inches. Now let’s take that circumference and multiply it by the valve lift. That computes the flow area

One cylinder-head component that is not as easily measured is the shape of the combustion chamber. Newer-model heads tend to take advantage of chamber shape in order to improve combustion efficiency. There’s no test procedure for this, but CNC-machined chambers tend to be more consistent than as-cast chambers, and shallow, heart-shaped chambers tend to be more efficient than older, deeper chambers. Continuing with our small-block Chevy example, compare a ’60s-vintage 64cc “fuelie” chamber with an iron Vortec head and then with a current LS3 chamber design to get an idea of how the chamber has progressed. This can have a dramatic effect on engine performance, as a well-designed chamber requires less total timing. LS engines typically make best power with less than 30 degrees of total ignition timing. This may not seem important, but as you shorten the lead time of the initial spark, the engine reduces the negative work required to push the piston against increasing cylinder pressure as it approaches TDC. A difference of 6 to 8 degrees can be worth measureable horsepower, assuming, of course, that the chamber can take advantage of that shorter ignition lead time. We hope we’ve given you some information you can chew on to supplement your own fact-gathering efforts. As the famous rock song goes: “Is the knowledge gained worth the price of the pain?”

Axle Play

Larry Soley; Istanbul, Turkey: I’m in Istanbul, Turkey, and it takes a while for me to get Car Craft. My wife forwards it from Wisconsin. The Apr. ’12 issue carried an article by Jeff Smith titled, “Junkyard Builder: Budget GM Rear Disc Brakes.” The closing sentence of the article (on page 74) reads, “Perhaps the biggest hassle in mounting this rear-brake conversion on an early car is pulling the rear cover to yank the C-clips so the rear axles can be removed.” Why do the axles need to be removed? There was no mention of this in the rest of the article. Thanks.

Jeff Smith: The axles have to be removed in order to remove the original drum-brake backing plates and to install the caliper mounting brackets. The drum-backing plates must be removed first—we just skipped that step.

2/2These C-clips fit in between the end of a C-clip axle and the inside of the side gears on the differential. They remain in place because the cross-pin prevents the axles from moving inboard and allowing the C-clips to fall out. By changing the width of the clips, you can select-fit a clearance between the axle ends and the cross-shaft.

A common complaint about rear-disc brake conversions is called piston knock-back, where excessive axle endplay pushes the caliper pistons into their bores, which creates a soft brake pedal that can cause major pedal travel before the rear-brake pistons regain their proper position. This is typically more of an issue with fixed-caliper brakes, but it’s worth discussing here because the fix is easy and cheap. We spoke with Tom at Tom’s Differentials, and he sells select-fit C-clips that can be used to set a minimal endplay clearance between the ends of the axles and the differential cross-shaft of 0.005 to 0.008 inch. These C-clips are high-strength forgings sold in various thicknesses. By varying the thickness of one or both clips, you can blueprint the endplay to the minimum spec and eliminate the problem of piston knock-back. The custom-fit clips are only $6 each.

GM Crate-Engine Warranty Update

Kevin Shafer; Chevrolet (GM) Performance Parts specialist & Powertrain Contact Center consultant: In the May ’12 issue of Car Craft, Jeff Smith wrote an article called “Saturday Night Slayer.” The article uses the PN 10067353 universal 350. The article asks, “Who would give you a three-year /100,000 mile warranty and all new parts? GM does if you leave the engine stock.”

There are two things that are incorrect. The GM crate engine PN 10067353 only carries the three-year/100,000-mile parts and labor warranty if installed in ’72 to ’85 models that were available with a small-block. The engine could be used in a Monza or Monte Carlo but not in an S10 or a Vega. Jeff Smith intends to install this engine in a ’66 Chevelle, which is not covered under the 3/100 but would have the 12-month/12,000-mile “parts-only” warranty. Since you are using nitrous, the warranty would be void, and Jeff points this out in the article. But if a reader doesn’t use nitrous and installs it “out of application,” they would not receive the three-year/100,000 mile warranty. If the reader is installing the engine in an application outside of the ’72 to ’85 application, a wiser choice is to use the 290hp PN 12499529 application. This would carry a 24-month/50,000-mile parts and labor warranty in any street-licensed vehicle, as long as no power-adder was used. The 12499529 290hp engine is similar to the 10067353 engine, but with a different camshaft installed, so the basic foundation of the build would not be different.

The second item to clarify is how changing parts affects the warranty. On the 10067353 engine, the warranty would be void if you change items, because it is an “OE” engine. However, the warranty is not void if you change items on the 290hp engine, since it is a Performance Parts engine. In the article, Jeff changed the camshaft. If the reader changes the camshaft, the only portion of the warranty that would be void is if the failure were related to the camshaft or the change. For example, if the front-cover gasket starts leaking, this would not be covered, since the cover was removed for the cam swap. If the head gasket failed, this would be a covered warranty, since a camshaft swap does not disturb the cylinder heads. Of course, any warranty goes out the door with power-adders. The 12499529 290hp engine may be a wiser purchase for the majority of builders. This seems like a really cool “low-buck” article.

Jeff Smith: Thanks to Kevin Shafer, who works under contract with GM on warranty issues to make the GM warranty clear. I wasn’t aware that you could change the cam and still have the short-block under warranty. I also had not paid attention to the fact that the warranty applied only to the later-model GM vehicles. This makes choosing either the Goodwrench engine or the 290hp motor that much better of a deal. Keep in mind that the time factor often runs out long before the miles do. That means you should bolt the engine in the vehicle right away after purchase rather than waiting five years like some of us!